Re: How can I user @cast in the user-space's program or have other ways to aasign valus to the user-space pointer to a structure.

[David Smith <dsmith at redhat dot com>]

Liu,

This is really a question for the systemtap list, not the utrace list.
Forwarding there.  Also see possible answer below.

On 03/26/2012 10:06 PM, Liu Tianhao wrote:

> I have a problem to cast a pointer to a structure in the user-spaceâs program.
> It always report âERROR: kernel write fault at 0x0000000000400675 (addr) near 
> identifier '@cast' at test.stp:3:8â.
> 
> Compile the source file and execute the stap command.
> liuth@liuthivb:~/$ gcc -g -o test test.c
> liuth@liuthivb:~/$ sudo stap -w -vg test.stp -c ./test
> Pass 1: parsed user script and 81 library script(s) using 
> 49344virt/22060res/2024shr kb, in 130usr/0sys/125real ms.
> Pass 2: analyzed script: 2 probe(s), 9 function(s), 0 embed(s), 0 global(s) 
> using 51992virt/23168res/2540shr kb, in 10usr/0sys/5real ms.
> Pass 3: using 
> cached /home/liuth/.systemtap/cache/5c/stap_5c288dc4a44724d509924f222aedb626_90
> 50.c
> Pass 4: using 
> cached /home/liuth/.systemtap/cache/5c/stap_5c288dc4a44724d509924f222aedb626_90
> 50.ko
> Pass 5: starting run.
> hello world
> call------------------------------call
> The value of a:[F] The value of b:[10]
> call------------------------------call
> ERROR: kernel write fault at 0x00000000004005b5 (addr) near identifier '@cast' 
> at test.stp:3:8
> Pass 5: run completed in 10usr/0sys/589real ms.
> Pass 5: run failed.  Try again with another '--vp 00001' option.
> 
> I have modified the test.stp as follows.
> probe process
> ("/home/liuth/worksource/ddtv/tracedrv/java/DDTVConfig/test").function
> ("funcStruct").call
> {
>        // compilation error
>        // @cast($pStruct, "struct TestStruct",   "test.h ")->a = 31
>        //@cast($pStruct, "struct TestStruct",   "test.h ")->b = 32
> 
>        // ERROR: kernel write fault at 0x00000000004005b5 (addr) near 
> identifier '@cast' at test.stp:3:8
>        //@cast($pStruct, "struct TestStruct",   "<test.h> ")->a = 31
>        //@cast($pStruct, "struct TestStruct",   "<test.h> ")->b = 32
> 
>        //  ERROR: kernel read fault at 0x000000200000001f (addr) near 
> identifier '$pStruct' at test.stp:5:60
>        //@cast(&$pStruct, "struct TestStruct",   "<test.h> ")->a = 31
>        //@cast(&$pStruct, "struct TestStruct",   "<test.h> ")->b = 32
> 
>        @cast($pStruct, "struct TestStruct")->a = 31
>        @cast($pStruct, "struct TestStruct")->b = 32
>        printf("The value of a:[%X] The value of b:[%X]\n", $pStruct->a, 
> $pStruct->b)
> }


Hmm, what happens when you just use the pointer directly, like this:

	$pStruct->a = 31
	$pStruct->b = 32


> The following are the program and the script.

> -------------------------------------------------------------------------------
> -------------------------------------------------------------------------------
> -----
> Header file test.h:
> #include <stdlib.h>
> #include <stdio.h>
> typedef struct TestStruct
> {
>    int a;
>    int b;
> }ST_Test_Struct;
> 
> //int  func(int a, int b, int c)
> int  func(ST_Test_Struct tmpStruct);
> int funcStruct(ST_Test_Struct* pStruct);
> 
> source file test.c:
> #include "test.h"
> int  func(ST_Test_Struct tmpStruct)
> {
>  return tmpStruct.a + tmpStruct.b;
> }
> 
> int funcStruct(ST_Test_Struct* pStruct)
> {
>         return pStruct->a + pStruct->b;
> }
> 
> int main(int argc, char** argv)
> {
> ST_Test_Struct tmpStruct = { 1,2 };
> func(tmpStruct);
> funcStruct(&tmpStruct);
> printf("hello world\n");
> return 0;
> }
> 
> script  test.stp:
> probe process
> ("/home/liuth/worksource/ddtv/tracedrv/java/DDTVConfig/test").function
> ("funcStruct").call
> {
>        @cast($pStruct, "struct TestStruct")->a = 31
>        @cast($pStruct, "struct TestStruct")->b = 32
>        printf("The value of a:[%X] The value of b:[%X]\n", $pStruct->a, 
> $pStruct->b)
> }
> probe process
> ("/home/liuth/worksource/ddtv/tracedrv/java/DDTVConfig/test").function
> ("func").call
> {
>        printf("call------------------------------call\n")
>        $tmpStruct->a =15;
>        $tmpStruct->b =16;
>        printf("The value of a:[%X] The value of b:[%X]\n", $tmpStruct->a, 
> $tmpStruct->b)
>        printf("call------------------------------call\n")
> }
> 
> 



-- 
David Smith
dsmith@redhat.com
Red Hat
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